iphone 6 sotrage upgeade 16 gb to 128 gb

The storage capacity of the phone is not changeable

To get a higher storage you will have to buy a new phone with the desired storage capacity

Your options may be:

1. Discuss with your carrier about any upgrade program they may offer

2. Sell your current phone and purchase a new one

By the way the maximum amount of RAM you can get in an iPhone 5 is 64 GB. So even if you sell the one you have currently you will not be able to purchase one with 128 GB of RAM.